I think it's bloating. I remember being 8 weeks and thinking I had a visible (although small) bump already...looking back it definitely wasn't visible to anyone but me. And I definitely lovingly rubbed that little tiny bloat bump
I also had weird "tightness"/cramps/round ligament type pain from week 5-9ish. I remember worrying when these feelings subsided that something was wrong but all was perfectly fine. Things move around/loosen up in early pregnancy to prepare your body for what is to come - I think your uterus expands and your placenta grows much faster than the actual baby (still a raspberry size or something at that time).